Why is there such a thing as default passwords?

Why in 2016 are people still shipping software and devices with default passwords? The recent IOT/Botnet that broke large chunks of the internet was entirely avoidable if the devices had been shipped without default passwords.

This is perfectly within the capability of a device manufactuer - even British Telecom (who have many many issues) have been shipping their devices with randomized passwords printed on a sticker on the device for years. It’s not hard to do that! With software it’s even easier you just force the user to pick a password and don’t ship them with admin/password or whatever you’ve decided is good enough.